1. Field of the Invention
The present invention relates to a fuel injection controller having a function of learning an injection characteristic of an injector.
2. Description of Related Art
It is common knowledge to measure a deviation of an actual injection characteristic of an injector of a diesel engine from a standard characteristic and to store the deviation in a fuel injection controller before the injector is shipped, for example, as described in JP-A-2000-220508. Thus, even if the actual injection characteristic is deviated from the standard characteristic because of an individual difference at the shipping stage of the injector, fuel injection control can be performed to compensate the measured deviation. Taking into consideration the fact that the deviation of the injection characteristic changes with pressure of fuel (fuel pressure) supplied to the injector, JP-A-2000-220508 describes measuring deviations of the injection characteristic in multiple ranges divided according to the fuel pressure and storing the deviations.
The measurement of the injection characteristic before the shipping of the product is performed before the injector is mounted to an internal combustion engine. Therefore, there is a possibility that it is difficult for the fuel injection control based on the measured values to realize an expected injection characteristic of the injector during output control of the engine. In addition to the individual difference, an aging is also a factor of the deviation of the injection characteristic peculiar to the injector from the standard characteristic. This makes it more difficult to realize the expected injection characteristic of the injector through the fuel injection control based on the measured values during the output control of the engine.
JP-A-2003-254139 describes dividing a fuel amount, which is required by feedback control, into equal amounts and injecting the divided amounts of the fuel in multiple times during idle rotation speed control. Based on a difference between the actual fuel amount at this time and a standard fuel amount, an injection characteristic of an injector regarding a minute amount injection such as a pilot injection of a diesel engine is learned. Thus, the injection characteristic of the minute amount injection can be learned. The learning is performed during the idle rotation speed control. Therefore, aging of the injector can also be handled. However, JP-A-2003-254139 cannot learn the injection characteristic over a wide range of the injection amount, which can be injected during the fuel injection control.